You already mentioned cash flow, and the only thing I'd add is that if you buy in a highly desirable area, then your cash flow on day one may be low, but with consistent rent increases over time could end up high ... this is VS buying in the ghetto with high cash flow on day one, but those rents rarely go up to even keep up with inflation so your cash flow diminishes over time.Then there is appreciation.

It may be a big deal to some, but what I came on this site for, I am getting; and that's knowledge and to talk to others who have my same desire.  

We have a lot of waterfront properties where I live and I am hoping I can snag something nearby the water to make it more desirable for STR's and LTR's alike.

If you can learn to pick the right tenants and the home is located in a desirable area, you may just be able to get a nice stream of income.

If she left, the unit was in reasonably good shape, and you got a new tenant quickly that is pretty desirable.

How desirable is the neighborhood; will you have a hard time trying to resale?

I hear your emotion in your post and the desire for satisfaction in "righting this wrong." 

What would be more desirable to you and why, 3 duplexes on one parcel of land or 6 units in one building on one parcel of land?

Have you run the numbers on your primary home to know whether it will cash flow at all, or meet your desire for it to cover some part of your new mortgage?

That's great, so long as you are local, and still have a desire to be an active participant in your rentals.